Electronic trigger



Jan 12, 1954 4 Sheets-Sheet 1 Original Filed Dec. 29, 1948 I um b m mm \N. 0 m0 33% 3 m y /Q R f v ,m m MQSQSE Q Q. L Wm! Q y. I... a b V J I Saw 6 &. l a km J u \\\w 1 mu m A M \N r {a 53 E Q QM E.

ATTORNEY 4 She ets-Sheet 2 C. A. BERGFORS ELECTRONIC TRIGGER j m mm! v n m R Nfl n R. a. 52 m EQAQQ l 7 Jan. 12, 1954 c. A. BIERGFORS Re. 23,770

' ELECTRONIC TRIGGER Original Filed Dec. 29. 1948 4 Sheet's -Sheet L'- ATTORNEY Reiuued Jan. 12, 1954 ELECTRONIC TRIGGER Carl A. Bergfora, Roslyn Heights, N. Y., asslgnor to International Business Machines Corporation, New York, N. Y., a corporation of New York Original No. 2,506,439, dated May 2, 1950, Serial No. 67,885, December 29, 1948. Application for reissue April 28, 1951, Serial No. 223.472

Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

8 Claims.

This invention relates to trigger circuits and more particularly to a high speed trigger of the dual-tube type having two conditions of stability.

In trigger circuits of the conventional dualtube type, the plate of each tube is connected to the control grid of the other tube. In such triggers, one of the chief limiting factors affecting the upper operating speed is the self-loading due to the cross-connected plates and grids.

Briefly, the invention employs four tubes including two tubes used as triggers and two as cathode followers. For the purpose of clarity of description, the former are referred to herein as trigger tubes and the latter as cathode follower tubes. Certain electrodes of one cathode follower tube are interposed between the plate of each trigger tube and the grid of the other trigger tube and vice versa.

Accordingly, it is a principal object of this invention to provide a novel trigger wherein the trigger performance is relatively unaffected by loading.

Another object is to provide a novel triggir of extremely high operating speed and low cu rent consumption comprising cathode followers for cross-coupling the tubes of the trigger.

Still another object is to provide a trigger circuit operable over the range from one cycle per second to more than one megaeycle per second.

A further object is to provide a high speed trigger operable over a wide range of supply voltages.

Another object is to provide novel means for reducing the efiect of input capacitance of a trigger.

Still another object is to provide a novel trigger having two stable conditions and using two grid controlled tubes with the plate of each connected to the control grid of the other wherein the time constant, which determines the time required to switch the trigger from one stable condition to the other, is decreased by connecting each control grid of the tubes with a cathode of a cathode follower tube.

A further object is to provide a novel trigger having two interconnected tubes wherein the load compensating effect of the low impedance circuit of a cathode follower [in] is utilized to decrease the undesirable efiects of heavy loading by the control grids of the tubes of the trigger.

A still further object is to provide a trigger having a pair of grid controlled tubes with the plate of each connected to the control grid of the other by means of a cathode follower.

Still another object is to provide a novel trig- 2 ger comprising cross-coupled tubes, and cathode followers to reduce the effect of input capacitance of the grids of the cross-coupled tubes.

Other objects of the invention will be pointed .out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of examples, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. 1 is an equivalent circuit diagram of a cathode follower with a pure resistance load;

Fig. 2" is a circuit diagram of one embodiment of a high speed trigger;

Fig. 3 is a circuit diagram of another embodiment;

Fig. 4 is a circuit diagram of a further embodiment, requiring a fewer number of voltage supply lines;

Fig. 5 is a graph illustrating the voltage on the control grids of certain tubes under certain assumed conditions; and

Fig. 16 is: grzfiph iilhiilsltrating the voltage on the con ro gri s o cer a tubes under ati i g conditions. actual oper roughout the drawings like arts a nated by like numerals. p re deslg Before proceeding to the description of the various embodiments, it is believed that a brief discussion of various aspects of a cathode follower circuit will greatly simplify the explanagiuoirsof the advantages of applicants novel cir- Referring to Fig. 1, there is illustrated the [equivalent] circuit diagram of a cathode follower with a pure resistance load.

By a simple mathematical analysis, an expression may be derived for the input capacitance of a cathode follower in terms of its circuit constants. In Fig. 1, the signal voltage e; is impressed on the control grid of the tube and the output voltage [6g] 81: appears across a cathode resistor Rk- The voltage between the control grid and cathode is egk. The capacitance between the control grid and cathode is represented by C 1; and the capacitance between the control grid and plate is represented by Cgp.

It is fundamental that the voltage amplification of any amplifier is the ratio of the output voltage to the input voltage. Therefore, according to the designations of Fig. 1, the voltage amplification A obtained in a cathode follower is the ratio of the cathode voltage er to the signal voltage e; or

pressed by the following equation:

Now, substituting the value of en express in (M) for en in (N) the following equation is obtained:

The charge Q, across any capacitor, is equal to the value of the capacitance times the voltage E across the capacitor; or

Q=CE (P) It follows that the charge on the control grid Q: due to the grid-cathode capacitance is ex- Qgk=cgkegk (Q) Now, substituting the value of en of (O) in (Q) Also. the charge Q; due to the grid-plate capacitance is expressed by the following equation:

and grid-plate capacitances, hence by adding (R) and (S) QB=QW+QIk=CIp eg+cgk (e -Ac (T) From (P) the capacitance C, may be written as:

It follows that the effective input capacitance of C; is obtained by dividing (T) by e hence,

Cg=Cgp+CgkACgk (V) In a similar manner, there may be derived the equation for the input capacitance of a triode amplifier having a pure resistance plate load. This equation is as follows:

Equation V indicates that the input capacitance of the cathode follower, is less than, the sum of the grid-plate and grid-cathode capacitances, by an amount equal to the voltage amplification times the grid-cathode capacitance. The substraction of the quantity AC in Equation V indicates that the cathode voltage is in phase with the, signal voltage applied to the control grid of the tube. This means that the feedback voltage through the grid-cathode capacitance is in phase with and tends to sustain the impressed signal voltage. Hence, in the cathode follower circuit, the feedback through the grid-cathode capacitance is equivalent to. a reduction in the input capacitance.

On the other hand, Equation W indicates that the input capacitance ofa triode plate-loaded amplifier, is greater than th sum of the gridplate and grid-cathode capacitance by an amount equal to the ,voltage amplification times the gridplate capacitance. The addition of the quantity (A0 indicates that the voltage applied to the control grid is 180 degrees out of phase with the plate voltage. This means that the feedback voltage through the grid-plate, capacitance opposes the impressed grid voltage. Hence, in the plate-loaded amplifier circuit, the grid-plate capacitance serves to increase the total input capacitance whereas, in the'cathode follower circuit, the grid-cathode capacitance is utilized to decrease the total input capacitance.

4 In order to more clearly understand the particular advantages obtained from the use of a cathode follower circuit, the values of input capacitances for a triode amplifier and a cathode follower, using the same type of tube, in both cases, will now be computed and compared.

The grid-cathode capacitance C of a 121)? type tube, including the capacitance of the socket. is approximately 1.80 micromicrofarads and the grid-plate capacitance C is approximately 1.75 micromicrofarads. The voltage amplification A of this 12AU7 tube, when used as a triode amplifier in a conventional trigger circuit is approximately 10, while the measured voltage amplification of this tube, used as a cathode follower, is 0.988. By substituting these values in Equation W the input capacitance C of this tube, as a triode plate-loaded amplifier, is found to be 21 micromicrofarads. However, by substituting the above values in Equation V the input capacitance C of this tube, used as a cathode follower, is found to be only 1.8 micromicrofarads.

From these computations it is seen that the input capacitance of this tube, as used in the conventional trigger, is almost twelve times that of this same tube as used in the cathode follower circuit. Hence, by connecting the plates of each trigger tube to the control grids of the cathode follower tubes, respectively, the capacitative load on the plates of the trigger tubes will be decreased by a factor of twelve. Also, since the cathode follower grid is driven only slightly positive with respect to cathode, loading due to grid current is reduced to a negligible quantity.

Further, the resistive component of load coupled to each other of the trigger tubes when employed with a cathode follower is 970,000 ohms as compared with 400,000 ohms when using a conventional trigger. Hence, the plate current loads, which, it is to be noted, are inversely proportional to the resistive components, are in the ratio of 2.4 to 1 between the conventional trigger and the novel cathode follower trigger of applicants device.

The effective output impedance of 12AU7 tubes employed as cathode followers can be shown to be approximately 360 ohms and since it is only 360 ohms, it is obvious that the trigger grids, although presenting relatively heavy loading, can easily be driven from the low impedance source. In other words, the current flowing in the cathode follower from its plate to cathode automatically adjusts itself to provide a substantially constant value of output voltage, notwithstanding the load presented by the control grid of the trigger tube.

Another important advantage of the cathode follower coupled trigger is that the trigger grids are effectively in parallel with the cathode follower tube cathodes. Thus the effective time constant of the trigger tube grid circuit is reduced permitting operation at higher pulsing rates.

Now referring more particularly to Fig. 2, the novel trigger device is shown, for example, as comprising trigger tubes i0 and ii and cathode follower tubes l2 and i3. These tubes are actually sections of a 12AU7 miniature twin'triode type tube but will be referred to herein. as tubes. to facilitate the description.

The cathodes of the tubes l0 and Ii I jareconnected through conductors II and i5, respectively, to a zero volt line iii. The plates of the tubes i0 and Ii are connected through resistors I1 and II, respectively, each of 20,000 ohms and also through a resistor I! of 15,000 ohms to a plus 250 volt line 20.

The plates of the cathode follower tubes I2 and I3 are connected to the plus 250 volt line 20 through conductors II and 22, respectively. and their cathodes are connected to the zero volt line I6, through resistors 24 and 25 respectively, each of 24,000 ohms. The cathode of tube I2 is coupled to the control grid of tube I through a capacitor 26 of 0.00005 microfarad and the cathode of tube I3 is coupled to the control grid of tube II through a capacitor 21 of 0.00005 microfarad.

The plate of tube III is connected also, through a conductor 23 and parallel connected resistor 23, of 220,000 ohms, and capacitor 30, of 0.00005 microfarad, to the control grid of tube I3. The control grid of tube I3 is connected through a resistor 3| of 750,000 ohms to a minus 250 volt line 32. The plate of tube II is similarly connected through a conductor 33 and parallel connected resistor 34, of 220,000 ohms, and capacitor 35, of 0.00005 microfarad, to the control grid of tube I2. The control grid of tube I2 is connected through a resistor 36 of 750,000 ohms to the minus 250 volt line 32.

Input terminal 31 is coupled through a capacitor 33 or 0.00025 microfarad and a conductor 33 to the junction of the resistors I1 and It with the resistor I3. The output terminal 40 is coupled through a capacitor 4| of 0.00025 microfarad and a conductor 42 to the cathode of tube I3. The grid of tube I0 is connected by resistors 43 and 44 of 20,000 ohms and 250,000 ohms, respectively to the minus 250 volt line 32. The cathode of tube I2 is connected to the control grid of tube I0 through a resistor 45 of 36,000 ohms connected to the junction of resistors 43 and 44. Similarly the control grid of tube II is connected through resistors 46 and 41 of 20,000 and 240,000 ohms, respectively, to the minus 250 volt line 32. The cathode of tube I3 is connected to the control grid of tube II through a resistor 48 of 36,000 ohms connected to the junction of the resistors 46 and 41.

While no reset means are shown, it is to be understood that such may be provided in any conventional manner and in accordance with the particular use to which the trigger is to be put. The trigger, as illustrated, when energized, will assume, by chance, one of its two stable condi-' tions. For the purposes of explanation, it is assumed that tubes I0 and I2 are initially nonconductive and tubes II and I3 conductive. This initial stable condition is referred to herein as the "on" condition. When tubes I0 and I2, become conductive, and tubes II and I3 non-conductive, the trigger is in its other stable condition, designated herein as the off condition.

When the trigger is fon," the potential at the plate of tube II is low and is transferred over the conductor 33 to the resistors 34 and 38. The consequent low potential present at the junction of resistors 34 and 35. is applied to the control grid of the cathode follower tube I2, connected thereto and is sufficient to maintain that grid below cutoff potential thereby rendering tube I2 non-conductive. The potential at the cathode of this tube and at the control grid of tube I0 is determined by the voltage divider consisting of the resistors 24, 45 and 44 connected between the zero volt line I and the minus 250 volt line 32. The voltage at the control grid of tube I0 is sufficiently negative to hold it below cutofl', to thus render it non-conductive. The resulting high potential at the plate of the tube It is transferred over the conductor 23 to the resistors 23 and 3|. The consequent high potential present at the junction of the resistors 23 and 3| is transferred to the control grid of tube I3, connected thereto and renders that tube conductive. With this cathode follower tube I3 conducting, its cathode potential is relatively high, as compared to that of tube I2, and the potential transferred to the control grid of tube I I is sufficient to keep it conductive. Thus the trigger remains "on until the potential conditions are changed by application of a negative pulse to input terminal 31.

A series of negative pulses are applied across the input terminal 31 and the zero volt line I5. These pulses are of suflicient amplitude and steep wave front to effect switching from either on" or off, to the other condition. The trigger illustrated is non-responsive to positive pulses of the same amplitude as that of the negative pulses.

While it is shown that switching oi the trigger is obtained by supplying pulses to the plate circult of the trigger tubes, such does not constitute part of novelty of this device. It is understood that the trigger may be switched by applying pulses to the control grids of the trigger tubes or in any other conventional manner.

Assuming, as stated above, that the trigger is on, the first negative pulse applied, over the input terminal 31, capacitor 38 and line 33, to the junction of the resistors I1 and I8 with the resistor I3, suddenly reduces the voltages on the plates of tubes I0 and II. When the voltage on the plate of tube II thus momentarily decreases, a negative pulse is transferred over the conductor 33 and the parallel connected resistor 34 and capacitor 35, to the control grid of the cathode follower tube I2 but sincethis tube is already non-conductive, this negative pulse has no eil'ect.

At the same time, a negative pulse is transferred from the plate of the tube Ill over the conductor 23 and the parallel connected resistor 23 and capacitor'30 to the control grid of the cathode follower tube I3. The control grid voltage 01 the cathode follower tube I3 is driven beyond the cutoff value by this negative pulse and a steep negative pulse is produced at its cathode. This steep negative pulse is transferred to the control grid of the conducting trigger tube I I driving it beyond cutoff, and thus all four tubes I0, II, I2 and I3 are momentarily non-conductive which comprises a very unstable condition. Since the trigger tubes I0 and II are both momentarily non-conductive, their anodes at this instant are at high potential causing the voltages on the control grids of the cathode follower tubes I2 and I3 to rapidly rise exponentially toward a final value.

When the voltage on the control grid, of the originally non-conductive tube I2, starts its exponential rise, it starts from a value of minus 40 volts and, if allowed to continue, would reach a value of approximately a plus 87 volts. At the same time, the voltage on the control grid of the originally conductive tube I3 is plus 40 volts and if allowed to continue to rise would reach a value of plus 60 volts.. In other words the voltage differential of the control grid of tube I2 is 12'! volts while that of tube I3 is only 20 volts.

Since the voltage difierential on the grid of the initially non-conducting tube is several time:

greater than the voltage diflerential appearing at the grid of the initially conducting tube, the voltage at the grid oIthe initially non-conducting tube will reach critical bias value first because the time constants of both circuits are substantially equal. Thus the trigger will reverse its stable condition in response to each input pulse applied rather than return to its former stable condition.

This is shown clearly from inspection of Fig. wherein the dotted line curve A represents the voltage on the control grid of tube I2 starting from minus 40 volts while the dottedline curve B represents the voltage on the control grid of tube I3 starting from plus 40 volts. These curves were traced from an oscilloscope and were obtained by increasing the negative bias voltages on the control grids of the tubes sufllciently to prevent the trigger from switching to its other stable condition in response to input pulses and therefore do not illustrate the actual voltages when the trigger is operating under normal conditions. Hence, as shrown by curves A and B, the voltages on the control grids of tubes I2 and I3 are shown as reaching final values of plus 87 volts and plus 60 volts, respectively. These curves are drawn to twice the scale of the curves actually traced from the oscilloscope.

The initial values of voltage, when the trigger is on, are shown in Fig. 5. As is seen from curve B, before zero time is reached, the voltage at the control grid of tube I3 is plus 60 volts while, as is seen from curve A, that at the control grid of the tube I2 is minus 20 volts. At zero time, a twenty volt negative pulse is applied to the control grids of the tubes I3 and I2 which reduces the voltage at those grids to plus 40 volts and minus 40 volts, respectively. It is seen from Fig. 5, that the curves A and B cross, before either reaches the plus 45 volt line. The 45 volt line represents the cathode follower grid potential when the trigger grid is at cutofl' bias. This means that the crossover occurs before either tube III or II has become conductive since the voltage on the cathode follower control grids must reach a value of plus 45 volts, to render the trigger tubes conductive.

In actual operation, when the trigger flips, these dotted curves A and B of Fig. 5 are not obtained. This is because of the fact that the first tube which becomes conductive, causes the trigger to assume the stable condition correspondplus 60 volts and the voltage on the control grid of the other cathode follower tubedecreases to a stable value of minus 20 volts. The solid line curves C and D of Fig. 6 are obtained under actual switching conditions and correspond respectively to the curves A and 'B, which were obtained when actual switching of the trigger was prevented. The actual voltage on the control grid of tube I2 when switching of the trigger from on to off occurs, is shown by the solid line curve C while the voltage on the control grid 'of tube I3 during the same period is shown by the solid line curve D.

As is seen, the curves showing the voltages on the control grids of tubes I2 and I3 during actual operation are approximately the same as when operation was prevented, if we exclude the portions occurring after the curve C crosses line 45. It is seen that the solid curve C ascends beyond the plus 45 volt line,

v 8 after it crosses the solid curve D. The curve B of Fig. 5 having much less slope than the curve A, would cross the plus 45 volt line later in time.

When the curve C ascends beyond the plus 45 volt line, the critical voltage is exceeded and tube I2 is rendered conductive. Hence, under actual flipping conditions, the voltage on the control grid of tube I2 continues to rise, not toward a final value of plus 87 volts as shown by dotted curve A of Fig. 5 but toward a value of plus 60 volts, as is seen from solid curve C of Figure 6. When tube I2 is thus rendered conductive, its cathode voltage increasesrapidly, which voltage is transferred over capacitor 26 and resistors 45 and 43 to the control grid of tube III to render it conductive. Its plate voltage decreases sharply and this decreased voltage is transferred over conductor 23 and parallel connected resistor 23 and capacitor 30, to the control grid of tube I3. This is seen from curve D representing the voltage on the control grid of tube I3, which declines sharply, as the curve C ascends beyond the plus 45 volt line. As is seen from curve D, the voltage at the control grid of tube I3 decreases until it reaches a final value of minus 20 volts.

The curves of Fig. 6 showing the voltage on the control grids of the cathode follower tubes l2 and I3 when the trigger is switched from on to "off" may also be employed to represent the voltage on these controy grids when the trigger is switched from off" to on. When the trigger is switched from "off" to on," the voltage on the control grid of tube I2 would be represented by the curves B and D and the voltage on the control grid of tube I3 by the curves A and C.

As set forth mathematically above, the input capacitance of a triode trigger tube is greater than the sum of the grid-cathode andgrid-plate capacitance but the input capacitance of the cathode follower tubes I2 and I3 is much less than the sum of the grid-cathode and grid-plate capacitance. The resulting permissible decrease in the capacitance used between the plates of the trigger tubes and the control grids of the cathode follower tubes means that the RC circuit used in the novel trigger circuit of the invention has a much lower time constant than that used in the conventional trigger. In other words, the switching of the present trigger requires less time and the trigger is therefore capable of higher speed operation. This is graphically represented by the extremely steep slope of the curve C showing the rapid increase of the control grid voltage on the tube which is switched from the nonconductive to the conductive state.

Resuming the detailed operation of the circuit of Fig. 2, when the second negative pulse is applied to the input terminal 31 the voltage on the plates of tubes I0 and II is again decreased. A negative pulse is transferred from the plate of tube III over the conductor 28 and parallel connected, resistor 29 and capacitor 30, to the control grid of the tube I3. However, since tube I3 is now non-conductive, this negative pulse has substantially no effect. At the same time, a. negative pulse is transferred from the plate of tube II over the conductor 33 and parallel connected resistor 34 and capacitor 35, to the control grid of conductive tube I2. This control grid is driven below cutoff and tube I2 rendered nonconductive to produce a steep negative pulse at its cathode. This steep negative pulse is transalmost immediately ferred overcapacitor 26 and resistors 45 and 43 9 tothecontrolgridoiconductivetube ll sothat this control grid is driven beyond cutofi to render the tube It non-conductive. At this point in the switching of the trigger. as in its switching iron: the "on" to the "oil" condition, all four tubes ll, II, it and II are non-conductive.

The voltages on the control grids of tubes I! and II rise toward a final value, under the control oi their respective RC circuits. It should be noted that the initial and final voltage values the control grid of tube It will now correspond to those values set iorth above for the control grid of tube It, when the trigger was switched from the "on" to the "oil" condition, in response to the first negative pulse applied to the input terminal 31. Also, the initial and final voltage values of the control grid .0! tube II will now correspond to those values given tor the control grid 0! tube II, when the trigger was switched from the "on" to the "oil condition, in response to the first negative pulse applied to input terminal 11.

In the same manner as that described in connection with tubes II and 12, when switched by the first negative pulse, the voltage on the control grid oi tube It rises above the critical value and that tube is rendered conductive. When tube l3 becomes conductive, the voltage on the control grid of tube I l rises above cutoi! and renders it conductive, to place the trigger in the "on condition.

- Subsequent negative pulses applied across input terminal 31 and zero volt line It, cause the trigger to switch from on" to "ofl and vice versa, alternately, as in response to the first and second negative pulses, respectively.

Referring to Fig. 3, the power supply arrangement is difierent from that used in Fig. 2. The plus 250 volt line 20 of Fig. 2 is replaced bythe plus 50 volt line 49 of Fig. 3. The cathodes of tubes l0 and H are still connected to a zero volt line IE but the tubes I2 and I! are connected via the resistors 24 and 25, respectively, to a minus 10 volt line 50 while the grids of tubes l2 and II are connected via resistors 36 and I I, respectively, to the minus 150 volt line II Further, the oathode of tube I2 is directly connected to the control grid of tube 10 by conductor 52 while the cathode oi tube l3- and the control grid of tube II are similarly connected by the conductor 53.

Referring to Fig. 4, the same circuit as in Fig. 3 is illustrated except that the cathode of tube I2 is connected to the control grid 01 tube 10 by means of a conductor 52 and also a parallel con-,

nected resistor 54 and capacitor 55. The cathode of tube I3 is also connected to the control grid of tube H through a conductor 53 and a parallel connected resistor 56 and capacitor 51. Resistors 54 and 56 each have a value of 20,000 ohms and the capacitors 5i and 51 each havea value of 0.00005 microfarad. Resistors 54 and it serve to provide a safe current limit through the control grids of tubes and II, respectively, when these tubes are in a stable conductive condition. The capacitors 55 and 51 provide a low impedance path for the higher order harmonics present in the steep wave front pulses normally transferred from the cathodes of the tubes l2 and I! to effect switching of the trigger tubes l0 and I I.

While the circuit shown in Fig. 2 illustrates one arrangement of the novel high speed trigger of the invention using a minimum number of supply lines, a wide variety of arrangements may be used without departing from the teachings o! the invention. For example, in Fig. 4, the minus 10 volt line It can be eliminated, cathode resisters II and II connected to the zero volt line II and grid bias resistors connected in series with but intermediatethe resistors ll and It and the minus 150 volt line 02. Such will require only two voltage supplies and the voltage dividers, esch'oi which is associated with the cathode ot one of the cathode iollower tubes and the control grid of one of the trigger tubes, permitting a wide choice or resistor values.

In each of Figs. 2, 3 and 4, the circuitarrangement produces a lower time, constant, by far, than in the conventional dual-tube trigger, as expressed succinctly in the mathematical discussion above. Also, since the cathode tollower has an extremely low output impedance, it is capable of driving the trigger grid to precisely reproduce any voltage variation applied to the cathode follower grid even though the cathode follower load is appreciable.

Also, the trigger can be operated over a wide range of supply voltages. For example, the trigger will operate with plate supply voltage as low as plus 16 volts and grid bias'supply' voltage of minus 20 volts. With a plate supply voltage of plus volts and a grid bias supply voltage of minus 100 volts the trigger was operated satisiactoriiy up to 1.39 megacycles. The maximum speed or operation was 1.6 mc., using plus 210 and minus 107 volts.

Although miniature triodes oi the 12AU'7 type were employed, and particular values of components were recited herein, it is to be understood that the invention is'by no means limited to such tubes and component values but that any suitable type tube and values of components may be employed without departing Irom the teachings of the invention.

While there have been shown and described and pointed out the fundamental novel ,ieatures oi the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the term and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A trigger circuit including first and second trigger tubes alternately conductive and nonconductive and vice versa to represent two stable conditions; plate resistors in the plate circuit of said tubes; a connection from said plate circuit to a source 01' pulses for efiecting a change in the stable condition 01' said trigger; third and fourth vacuum tubes each having their plates connected directly to a voltage source and their cathodes connected to another voltage source through a resistor in the cathode circuit of each; a resistor and capacitor in parallel between the plate or said first tube and the control grid of said third tube for rendering said third tube conductive when said first tube is non-conductive and rendering said third tube non-conductive when said first tube is conductive; a connection from the cathode 01 said third tube to the control grid of said second tube for rendering said second tube conductive and non-conductive, respectively, as a result 01' the conduction and non-conduction of said third tube, said connection including a resistor and capacitor in parallel; a resistor and capacitor in parallel between the plate of said.

earro 11 tube for rendering said fourth tube conductive when said second tube is non-conductive and rendering said fourth tube non-conductive when said second tube is conductive. and a connection from the cathode oi said fourth tube to the control grid of said iii-st tube tor rendering said first tube conductive and non-conductive, respectively,

, as a result of the conduction and non-conduction or said fourth tube, said connection including a res stor and capacitor in parallel.

2. The circuit of claim 1 including bias resistors connected to the controlsrids of the tubes.

3. A trigger circuit includinz first and second tri ger tubes alternately conductive and nonconductive and vice verse to represent two stable conditions: a resistor connected at one end to the plate 01 each tube; a resistor connected to a source oi plate supply voltaae at one end and at its other end to the other ends of the resistors connected to the plates of the tubes; third and fourth tubes each having their plates connected directly to said source 01' plate supply voltage; a cathode voltage source connected directly to the cathodes of said triager tubes and through res sters to the cathodes of the third and fourth tubes: a resistor and capacitor in parallel be-' tween the late at said first tube and the control grid oi said third tube for rendering said third tube conductive when said first tube is non-con; ductive and rendering said third tube non-conductive when said first tube is conductive: a resistor and capacitor in parallel between the plate oi. said second tube and the control grid at the fourth tube for renderine said fourth tube conductive when said second tube is non-conductive and rendering said fourth tube non-conductive when said second tube is conductive: a capacitive connection from the cathodes of the third and fourth tubes to the control grids of the second and first tubes, respectively; control arid bias resistors connected from the control grids of said tubes to a source of voltage and a resistive connection from the control grid bias resistors 01 the first and second tubes to the cathodes o! the fourth and third tubes respectively.

4. An electronic switching circuit including first and second grid controlled tubes, alternately automatically conductive and non-conductive and vice versa, and third and fourth grid controlled tubes corresponding tosaid first and second grid controlled tubes respectively and operating as a cathode follower, the third tube having its control grid connected through a resistor and capacitor in parallel only to said first grid controlled tube and the fourth tube having its control grid connected through a resistor and capacitor in parallel only to said second grid controlled tube so that a change in the conduction of either of said first and second tubes controls the conduction of the cathode follower tube having its control grid connected thereto.

5. In an electronic switch having two gr d controlled tubes and two, stable conditions alternately assumed, third and fourth grid controlled tubes, each. operated as a cathode follower, the third tube having its control grid connected only to said first grid controlled tube through a resistor and capacitor in parallel and the fourth tube having its control grid connected only to said second grid controlled tube through a resistor and capacitor in parallel; a first connection com rising a resistor and a capacitor in para lel between the cathode of the third tube and the control grid of the second tube; and a second connection comprising a resistor and a capacitor in parallel between the cathode of the fourth tube and the control grid of the first tube.

0. In a trigger circuit having two grid controlled tubes and two stable condition: alternately assumed, a cross-connection from the anodeofeachtubetothecontmlgridofths other, each said cross-connection including an inter-electrode space of a thermionic tube having at least a cathode, a grid, and an anode, an electrical connection comprising a capacitor and resistor in parallel between the cathode of the thermionic tube and the grid of the respective grid controlled tube, and a connection between the grid of the thermionic tube and the anode of the respective grid controlled tube.

1. A trigger circuit comprising a 1m: and second grid controlled electron discharge device each having at least an anode and an anode load resister, a first and second cathode follower having at least a grid, a cathode, an anode and a resistor connected to the cathode and in series with a source of anode potential and the cathode fol- ,lower inter-electrode space, means connecting ond cathode follower to the anode of the second electron discharge device and the grid of the first electron discharge device.

8. In an electronic switching circuit, a first and a second vacuum tube each having at least an anode, a cathode and a control electrode, a source of anode potential and an impedance connected between the positive pole of the said anode potential source and each of the anodes of the said first and second vacuum tubes, a first and a second cathode follower each having at least a cathode, a grid, an anode and a load resistance in series with the cathode, a connection comprising a capacitor and resistor in parallel between the grid of the first cathode follower and the anode of the first electron vacuum tube, a connection from the first cathode follower load resistance to the grid of the second vacuum tube, a connection comprising a capacitor and resistor in parallel between the anode of the second vacuum tube and the grid of the second cathode follower, a connection between the second cathode follower load resistance and the grid of the first electron vacuum tube, and means for impressing the potential of the anode potential source across each series network comprising a cathode follower inter-electrode space and the respective cathod follower load resistance.

CARL A. BERGFORS.

Beterences Cited in the me of this patent or the original patent UNITED STATES PATENTS Number Name Date 2,404,047 Flory et a1 July 16, 1946 2,441,579 Kenyon May 18, 1948 2,454,815 Levy Nov. 30, 1948 2,540,539 Moore Feb. 6, 1951 2,550,116 Grosdofl Apr. 24, 1951 FOREIGN PATENTS Number Country Date 587,940 Great Britain May 9, 1947 

